1. Field of the Invention
The present invention relates to a method for manufacturing a wiring board used for mounting a semiconductor element such as a microchip.
2. Description of Related Art
In recent years, amid the advance in a high performance and thinning of electronic devices such as portable video game players and communication devices, build-up wiring boards are present as high-density wiring boards used for these devices. General build-up wiring boards have a configuration such that insulating layers and wiring conductors are alternately laminated on both surfaces of a core substrate having a thickness of about 0.2 to 2.0 mm. Core substrates are formed by a resin substrate and a wiring conductor. The resin substrate is obtained by impregnating an electric insulating material such as epoxy resin in a glass fiber. The wiring conductor is made of a copper foil. The insulating layer is formed of resin having a thickness of about 10 to 100 μm, and the wiring conductor is formed by a plated metal layer having a thickness of about 5 to 50 μm.
Although high-density wiring is enabled in such a general build-up wiring board, a core substrate having a thickness of about 0.2 to 2.0 mm is used. For this reason, it is difficult to thin the entire thickness of wiring boards.
For example, Japanese Patent No. 4273895 describes a method for manufacturing a thin and high-density circuit board without a core substrate. In this method, ultrathin copper foils with a carrier copper foil are laminated on supporting substrates of the uniform size. The carrier copper foil holds the ultrathin copper foil via a release layer. A plurality of insulating layers and a plurality of wiring conductors made of a plated metal layer are alternately laminated on the ultrathin copper foil. Thereafter, the circuit board that is being manufactured is separated into the ultrathin copper foil and the carrier copper foil so that the ultrathin copper foil is removed.
However, in the method described in Japanese Patent No. 4273895, since the ultrathin copper foil with the carrier copper foil and the supporting substrate have the same size, a boundary between the carrier copper foil and the ultrathin copper foil is exposed outside. For this reason, for example, a plating solution for forming a wiring conductor occasionally infiltrates both the carrier copper foil and the ultrathin copper foil through the boundary therebetween. When the plating medical solution infiltrates in such a manner, adhesion between the carrier copper foil and the ultrathin copper foil is weakened, and thus a circuit board that is being manufactured is occasionally peeled from a supporting substrate. For this reason, fabrication yield of the wiring board comes down, and circuit boards cannot be efficiently manufactured.